1. Field of the Invention
The present invention relates to improvements in the intake, exhaust and combustion characteristics of an engine.
2. Description of the Related Art
It has not been possible to vary the time required for a portion of each of the intake, compression, expansion and exhaust strokes of an internal combustion engine with regard to another portion. For that reason, it has not been possible to solve the following five problems about an internal combustion engine. The first to fourth problems occur because a portion of each piston stroke requires a short time. The fifth problem occurs because another portion of each piston stroke requires a long time.
First Problem
As shown in FIG. 12, the valve lift is radically smaller during an initial period M1 in each intake stroke than during a middle period M2 of it. As a result, in a four-cycle engine, the amount of gas sucked into each cylinder during the initial period M1 decreases as the engine speed increases. In turn, the pressure in the combustion chamber becomes lower than the pressure in the crankcase. This results in a force acting away from the crankcase toward the combustion chamber. During the initial period M1, the piston continues to move away from the cylinder head against this force. This results in a decrease in torque because of an increase in negative work, as well as an increase of the loss caused by the intake resistance.
FIG. 11 of the accompanying drawings is substantially identical with FIG. 1 on page 90 of the November, 1995 (Issue No. 434) issue of a magazine entitled “Internal Combustion Engine” published by Sankaido. FIG. 11 additionally shows the maximum torque points L1 and L2. At engine speeds higher than those at the maximum torque points L1 and L2, the torque is lower than these points. One of the causes of the torque drop is the increased loss caused by the exhaust resistance.
Second Problem
As shown in FIG. 12, the valve lift is radically smaller during an initial period M1 in each exhaust stroke as well than during a middle period M2 of it. As the engine speed increases, the time from opening the exhaust valve until the bottom dead center of the exhaust stroke becomes shorter. This increases the pressure in the cylinder at the bottom dead center, increasing the loss caused by the exhaust resistance after the piston reaches the bottom dead center.
Third Problem
The thermal efficiency is mainly governed by the combustion speed of the mixture and the descending speed of the piston. The descending speed is governed by the combustion speed. Therefore, it has been impossible to slow down only the descending speed. For that reason, it has been impossible to improve the thermal efficiency.
Fourth Problem
In a two-cycle engine, as the engine speed increases, the time from opening the exhaust port to opening the scavenging port becomes shorter. This causes the pressure in the cylinder to be high when a scavenging stroke starts. As the engine speed increases, this reduces the efficiency of scavenging the residual exhaust gas inside the cylinder with the scavenging flow. As a result, the mixture filling rate drops, and the torque decreases.
Fifth Problem
In a spark ignition type internal combustion engine, if the pressure history becomes too high through the combustion in a portion of the combustion chamber, all ends of the flame propagation paths self-ignite at the same time. This destroys the extinguishing layers adjoining the walls of the combustion chamber, so that there is an increase in the heat flowing into the chamber walls. As a result, the chamber walls melt down. Normally, the compression ratio has a low setting so that such knocking does not occur. This restricts the improvement of thermal efficiency.